What condition is required for Closed Loop operation?

• A. The O2 sensor must be sending a switching voltage
• B. The MAP sensor must read atmospheric pressure
• C. The MAF sensor must be warmed up
• D. The engine must be in open loop

Answer: (A)

Closed loop operation depends on feedback from the exhaust oxygen sensor. When the O2 sensor is heated to its operating temperature and actively switching between richer and leaner voltages, the engine control module uses that signal to continuously adjust fuel metering and keep the air–fuel ratio at the stoichiometric point. That switching signal is what signals that feedback-based control is active.

If the oxygen sensor isn’t switching, the ECU can’t use its feedback to trim fuel, so the system would be in open loop. The MAP sensor reading atmospheric pressure or the MAF sensor simply being warmed up aren’t, by themselves, the condition that defines closed loop. Open loop is the state opposite to closed loop, where no sensor feedback is used for fueling.